A general production process of a rim will be explained based on FIG. 4. A rolled steel plate 1 wound in a roll shape is cut in given dimensions to form a blank 2. The blank 2 is roll-formed to cause the cut surfaces on each side to confront each other. The confronting sections are flash butt welded to form a cylindrical body 3. Subsequently, the cylindrical body 3 is rim-formed to from a rim 4.
When the blank 2 is roll-formed to cause the cut surfaces on each side to confront, the cut surfaces 2a are open as shown in FIG. 5(a) and the surface to be inserted between electrodes is not flat. Accordingly, the cut surfaces 2a, 2a are not welded well by the flash butt welding. In the conventional production process, as shown in FIG. 5(b), bending is carried out to make the cut surfaces 2a, 2a parallel, wherein the surface to be inserted between the electrodes is made flat for flash butt welding. In the case of the flash butt welding, as shown in FIG. 5(c), an excess weld metal of a weld bead 5 is produced between the inside and outside of a welded section. Accordingly, the excess weld metal of the weld bead 5 is removed by after-treatment.
Japanese Unexamined Patent Publication No. HEI 3-275289 (1991) suggests laser welding as a means for welding.
By adopting the laser welding, the weld time is reduced and cutting of the bead of the excess weld metal after welding is not required. However, a bending process is still necessary to make the cut surface of the blank parallel. In the case where the bending process is not performed, fillers for filling in the gap are required during laser welding. This decreases the efficiency of rim production.
It is therefore an object of the present invention to provide an improved method for producing a circular body such as a rim forming a tire wheel.